This invention relates to an auxiliary vent component that is to be added to a pressurized deaerator unit in a boiler feedwater system. The vent component is designed to eliminate non-condensible gases from the boiler feedwater system while preventing escape of steam during the purging process. In particular, the auxiliary component comprises a steam condensate recovery component for the gas vent in pressurized deaerator units. Generally, deaerator units that are not directly vented to atmosphere are classified as pressurized deaerators. The pressurized deaerators include safety vents to prevent excessive internal pressures and a non-condensible gas metering vent that provides a substantial degree of safety during use. The use of a condensate recovery component in a pressurized deaerator is desireable because the condensate can be directly returned to the deaerator unit with minimal loss of thermal energy. The auxiliary steam condensate recovery component proposed, is used in the deaerator unit of pressurized boiler feedwater systems where operating characteristics allow recovered steam condensate to be returned to the feedwater system as preheated return water.
A deaerator unit is a device to remove non-condensible gases from the feedwater that is supplied to a boiler unit. Non-condensible gases are generated in a system through chemical reactions with the high temperature feedwater tubes of a boiler, or admitted with the supply of makeup water from a water source. In particular, carbon dioxide is generated from carbonates present in circulating water. Air, carbon dioxide and other non-condensible gases must be continuously purged from the feedwater system. Substantial effort has been expended for development of highly efficient systems for stripping and purging to atmospheric such non-condensible gases from the circulating water in a deaerator unit.
In general, deaerators are rated for dissolved gas content as either 0.03 cc per liter or 0.005 cc per liter deaerators. The latter rated deaerator is the most effective in removing dissolved gases. In the final purge of the non-condensible gases from the deaerator unit, steam is frequently carried with the non-condensible gases and vented to the atmosphere with the resultant loss of the thermal energy from the heat content of the lost condensate. Furthermore, the requirement for addition of makeup water from an ambient temperature source not only requires preheating, but the stripping of dissolved gases from the added makeup water. In a typical pressurized deaerator unit of ordinary efficiency, approximately 1% of the steam used in the deaeration process is lost. In a boiler operating at a steam rate of 100,000 pounds per hour that obtains 100% of its makeup water from an ambient temperature source, it is estimated that 16,000 pounds per hour of steam is required for preheating the makeup water. With a hypothetical boiler efficiency of 80%, and a heating cost of 0.4 dollars per therm, the yearly cost from thermal losses from escaping steam is approximately $8,000 per year, per unit.
In the deaerator unit disclosed as an exemplar for inclusion of the subject steam condensate recovery component, a highly efficient system has been devised to purge non-condensible gases from the deaerator unit. Although designed in part to substantially reduce losses of vapor and condensible steam, steam loss can virtually be reduced to zero by the addition of the subject steam condensate recovery component. It is to be understood that the efficient deaerator disclosed is used to describe the best mode contemplated for use of the steam recovery component, but that any conventional pressurized deaerator unit can be equipped with the steam recovery component where recovered condensate can be returned to the unit.